1. Field of the Invention
The present invention relates to an improvement in the recording accuracy reliability of a pen recorder.
2. Discussion of the Background
In a conventional closed-loop-controlled pen recorder, when a pen is to be moved to a recording position corresponding to an analog input signal, an amount of motion of the pen is detected as an angular interval by a potentiometer or the like, and the angular interval is fed back to a differential amplifier for detecting an error. In this case, like a slide-wire resistor, after the potentiometer has been operated for a certain period of time, an electrical contacting state at its sliding portion sometimes becomes poor. When poor contact occurs, the pen cannot be accurately controlled to be in the proper position defined by the analog input signal, thereby degrading the recording accuracy and operational reliability, and shortening the service life of the recorder. In addition, in the case of a multi-pen type recorder, since potentiometers must be provided for a plurality of pens, the recorder is necessarily larger. Furthermore, when recording accuracy is to be improved by using a potentiometer of a high-accuracy type, the cost is increased.
On the other hand, the inventor of the present application has considered an open-loop-controlled pen recorder which uses a stepping motor, and calculates the step number and a step rotation direction for moving a pen to a new recording position, in accordance with data of the previous and new recording positions, thereby performing a recording operation. However, in a pen recorder of this type, when a pen position is erroneously deviated for some reason, the pen cannot return from the deviated position to a correct recording position, so that reliable recording cannot be obtained thereafter.
Thus, in the conventional closed-loop-controlled pen recorder, a problem is posed in terms of the reliability, accuracy, and service life of a potentiometer for detecting a pen position, which is required for each pen. In a multi-pen type recorder, the recorder is enlarged in size by adopting a plurality of potentiometers, and the cost is increased. On the other hand, in the above open-loop-controlled pen recorder, when the pen position is erroneously deviated, reliability of recording data obtained thereafter will be lost.